Method for activating pscell and scell in mobile communication system supporting dual connectivity

ABSTRACT

The present disclosure relates to communication methods and systems for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system utilizing technology for Internet of Things (IoT). The present disclosure is applicable to intelligent services utilizing 5G communication technology and IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A Secondary Cell (SCell) method and apparatus for activating an SCell are provided for use in a mobile communication system supporting dual connectivity. The method includes receiving a control message instructing activation of at least one SCell, determining whether the SCell is a primary SCell (pSCell) based on the control message, monitoring, when the SCell is the pSCell, a Physical Downlink Control Channel (PDCCH) of the pSCell, and reporting, after starting PDCCH monitoring, Channel Status Information (CSI) for the SCell.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit under 35 U.S.C. §119(a) of a Koreanpatent application filed on May 8, 2014, in the Korean IntellectualProperty Office and assigned Serial number 10-2014-0055111, and of aKorean patent application filed on Nov. 18, 2014, in the KoreanIntellectual Property Office and assigned Serial number 10-2014-0160996,the entire disclosures of each of which are hereby incorporated byreference.

TECHNICAL FIELD

The present disclosure relates to a method and apparatus for activing aSecondary Cell (SCell) in a mobile communication system supporting dualconnectivity.

BACKGROUND

To meet the demand for wireless data traffic having increased sincedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a ‘Beyond 4G Network’ or a‘Post LTE System’. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, the beamforming,massive multiple-input multiple-output (MIMO), Full Dimensional MIMO(FD-MIMO), array antenna, an analog beam forming, large scale antennatechniques are discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud Radio Access Networks(RANs), ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,Coordinated Multi-Points (COMP), reception-end interference cancellationand the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) andsliding window superposition coding (SWSC) as an advanced codingmodulation (ACM), and filter bank multi carrier (FBMC), non-orthogonalmultiple access(NOMA), and sparse code multiple access (SCMA) as anadvanced access technology have been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the Internetof Things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The Internet ofEverything (IoE), which is a combination of the IoT technology and theBig Data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology”,“wired/wireless communication and network infrastructure”, “serviceinterface technology”, and “Security technology” have been demanded forIoT implementation, a sensor network, a Machine-to-Machine (M2M)communication, Machine Type Communication (MTC), and so forth have beenrecently researched. Such an IoT environment may provide intelligentInternet technology services that create a new value to human life bycollecting and analyzing data generated among connected things. IoT maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing Information Technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies such asa sensor network, Machine Type Communication (MTC), andMachine-to-Machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud RadioAccess Network (RAN) as the above-described Big Data processingtechnology may also be considered to be as an example of convergencebetween the 5G technology and the IoT technology.

Mobile communication systems were developed to provide the subscriberswith voice communication services while moving about. With the rapidadvance of technologies, the mobile communication systems have evolvedto support high speed data communication services beyond the earlyvoice-oriented services. However, the limited resource and userrequirements for higher speed services in the current mobilecommunication system spur the evolution to more advanced mobilecommunication systems.

Meanwhile, dual connectivity is an operation where a given UserEquipment (UE) consumes radio resources provided by at least twodifferent network points connected with non-ideal backhaul. For example,a UE may connect to a macro evolved Node B (eNB) and a small (pico) eNBthat are playing different roles to receive a service.

The dual connectivity is an issue under discussion in variouscommunication standardization organizations.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present disclosure.

SUMMARY

Aspects of the present disclosure are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentdisclosure is to provide a method and apparatus for activating aSecondary Cell (SCell) efficiently in a mobile communication systemsupporting the dual connectivity.

Another aspect of the present disclosure is to provide a method andapparatus for the primary SCell (pSCell) and SCells for efficientcommunication in a mobile communication system supporting the dualconnectivity.

In accordance with an aspect of the present disclosure, an SCellactivation method of a terminal supporting dual connectivity isprovided. The SCell activation method includes receiving a controlmessage instructing activation of at least one SCell, determiningwhether the SCell is a pSCell based on the control message, monitoring,when the SCell is the pSCell, a Physical Downlink Control Channel(PDCCH) of the pSCell, and reporting, after starting PDCCH monitoring,Channel Status Information (CSI) for the SCell.

In accordance with another aspect of the present disclosure, an SCellactivation apparatus of a terminal supporting dual connectivity isprovided. The SCell activation apparatus includes a transceiverconfigured to communicate with at least one network node and acontroller which controls the transceiver to receive a control messageinstructing activation of at least one SCell, to determine whether theSCell is a pSCell based on the control message, to monitor, when theSCell is the pSCell, a PDCCH of the pSCell, and to report, afterstarting PDCCH monitoring, CSI for the SCell.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a diagram illustrating the architecture of a Long TermEvolution (LTE) system according to an embodiment of the presentdisclosure;

FIG. 2 is a diagram illustrating a protocol stack of the LTE systemaccording to an embodiment of the present disclosure;

FIG. 3 is a diagram illustrating the concept of the intra-evolved Node B(eNB) carrier aggregation adopted to the LTE system according to anembodiment of the present disclosure;

FIG. 4 is a diagram illustrating the concept of the inter-eNB carrieraggregation adopted to the LTE system according to an embodiment of thepresent disclosure;

FIG. 5 is a diagram illustrating connection structures of a Packet DataConvergence Protocol (PDCP) entity in the LTE system according to anembodiment of the present disclosure;

FIG. 6 is a diagram illustrating a configuration of User Equipment (UE)capability information for dual connectivity according to an embodimentof the present disclosure;

FIG. 7 is a diagram illustrating a configuration of UE capabilityinformation for dual connectivity according to an embodiment of thepresent disclosure;

FIG. 8 is a signal flow diagram illustrating a dual connectivityconfiguration method according to an embodiment of the presentdisclosure;

FIG. 9 is a flowchart illustrating a UE capability report procedure inthe dual connectivity configuration method of FIG. 8 according to anembodiment of the present disclosure;

FIG. 10 is a flowchart illustrating a UE operation according to anembodiment of the present disclosure;

FIG. 11 is a flowchart illustrating a UE operation when the TimingAdvance (TA) timer of a TA Group (TAG) expires according to anembodiment of the present disclosure;

FIG. 12 is a flowchart illustrating another UE operation according to anembodiment of the present disclosure;

FIG. 13 is a flowchart illustrating the UE operation according to anembodiment of the present disclosure;

FIG. 14 is a block diagram illustrating a configuration of the UEoperating in an LTE system according to an embodiment of the presentdisclosure; and

FIG. 15 is a block diagram illustrating a configuration of the eNBoperating in the LTE system according to an embodiment of the presentdisclosure.

The same reference numbers are used to represent the same elementsthroughout the drawings.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the present disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thepresent disclosure. In addition, descriptions of well-known functionsand constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of the presentdisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of the presentdisclosure is provided for illustration purpose only and not for thepurpose of limiting the present disclosure as defined by the appendedclaims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

As used herein, terms such as “first,” “second,” etc. are used todescribe various components. However, it is obvious that the componentsshould not be defined by these terms. The terms are used only fordistinguishing one component from another component. For example, afirst component may be referred to as a second component and likewise, asecond component may also be referred to as a first component, withoutdeparting from the teaching of the inventive concept. The term “and/or”used herein includes any and all combinations of one or more of theassociated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentdisclosure. It will be further understood that the terms “comprises”,“comprising”, “includes” and/or “including”, when used herein, specifythe presence of stated features, integers, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, operations, elements, components, and/or groups thereof.

Unless otherwise defined herein, all terms including technical orscientific terms used herein have the same meanings as commonlyunderstood by those skilled in the art to which the present disclosurebelongs. It will be further understood that terms, such as those definedin commonly used dictionaries, should be interpreted as having a meaningthat is consistent with their meaning in the context of thespecification and relevant art and should not be interpreted in anidealized or overly formal sense unless expressly so defined herein.

The present disclosure provides a signal transmission/reception methodand apparatus for use in a mobile communication system supportingmultiple carriers.

Also, the present disclosure provides a signal transmission/receptionmethod and apparatus for use in the mobile communication systemsupporting inter-evolved Node B (eNB) Carrier Aggregation (CA).

The signal transmission/reception apparatus and method of the presentdisclosure is applicable to various types of communication systems suchas Long-Term Evolution (LTE) mobile communication system, LTE-Advanced(LTE-A) mobile communication system, High-Speed Downlink Packet Access(HSDPA) mobile communication system, High-Speed Uplink Packet Access(HSUPA) mobile communication system, 3^(rd) Generation PartnershipProject 2 (3GPP2) High Rate Packet Data (HRPD) mobile communicationsystem, 3GPP2 Wideband Code Division Multiple Access (WCDMA) mobilecommunication system, 3GPP2 CDMA mobile communication system, Instituteof Electrical and Electronics Engineers (IEEE) 802.16m communicationsystem, Evolved Packet System (EPS), and Mobile Internet Protocol(Mobile IP) system.

First, an LTE system according to an embodiment of the presentdisclosure is described with reference to FIG. 1.

FIG. 1 is a diagram illustrating the architecture of an LTE systemaccording to an embodiment of the present disclosure.

Referring to FIG. 1, the radio access network of the LTE system includeseNBs 105, 110, 115, and 120, a Mobility Management Entity (MME) 125, anda Serving-Gateway (S-GW) 130. The User Equipment (UE) 135 connects to anexternal network via the eNBs 105, 110, 115, and 120, and the S-GW 130.

In FIG. 1, the eNBs 105, 110, 115, and 120 correspond to the legacy nodeBs of the Universal Mobile Telecommunications System (UMTS) system. TheeNBs 105, 110, 115, and 120 allow the UE 135 to establish a radiochannel and are responsible for functions more complicated as comparedto the legacy node B.

In the LTE system, all the user traffic services including real timeservices such as Voice over IP (VoIP) are provided through a sharedchannel and thus there is a need of a device to schedule data based onthe state information (such as buffer status, power headroom status, andchannel condition of the UE), the eNBs 105, 110, 115, and 120 beingresponsible for such functions. Typically, one eNB controls a pluralityof cells. In order to secure a data rate of up to 100 Mbps, the LTEsystem adopts Orthogonal Frequency Division Multiplexing (OFDM) as aradio access technology. Also, the LTE system adopts Adaptive Modulationand Coding (AMC) to determine the modulation scheme and channel codingrate in adaptation to the channel condition of the UE.

The S-GW 130 is an entity to provide data bearers, e.g., it establishesand releases data bearers under the control of the MME 125. The MME 125is responsible for mobility management of UEs and various controlfunctions and may be connected to a plurality of eNBs. A description ismade of the protocol stacks of the LTE system according to an embodimentof the present disclosure with reference to FIG. 2.

FIG. 2 is a diagram illustrating a protocol stack of the LTE systemaccording to an embodiment of the present disclosure.

Referring to FIG. 2, the protocol stack of the LTE system includesPacket Data Convergence Protocol (PDCP) layer 205 and 240, Radio LinkControl (RLC) layer 210 and 235, Media Access Control (MAC) layer 215and 230, and Physical (PHY) layer 220 and 225.

The PDCPs 205 and 240 are responsible for IP headercompression/decompression, and the RLCs 210 and 235 are responsible forsegmenting the PDCP Protocol Data Unit (PDU) into segments inappropriate size for Automatic Repeat reQuest (ARQ) operation.

The MACs 215 and 230 are responsible for establishing connection to aplurality of RLC entities so as to multiplex the RLC PDUs into MAC PDUsand demultiplex the MAC PDUs into RLC PDUs. The PHYs 220 and 225 performchannel coding on the MAC PDU and modulate the MAC PDU into OFDM symbolsto transmit over radio channel or perform demodulating andchannel-decoding on the received OFDM symbols and deliver the decodeddata to the higher layer.

A description is made of inter-eNB CA adopted to the LTE systemaccording to an embodiment of the present disclosure hereinafter withreference to FIG. 3.

FIG. 3 is a diagram illustrating the concept of the intra-eNB CA adaptedto the LTE system according to an embodiment of the present disclosure.

Referring to FIG. 3, an eNB 305 transmits and receives signals throughmultiple carriers across a plurality of frequency bands. For example,the eNB 305 can be configured to use the carrier 315 with the centerfrequency of f1 and the carrier 310 with the center frequency of f3.

If CA is not supported, the UE 330 must transmit/receive data using onlyone of the carriers 310 and 315. However, the UE 330 having the CAcapability can transmit/receive data using both the carriers 310 and 315concurrently. The eNB can increase the amount of the resources to beallocated to the UE having the CA capability in adaptation to thechannel condition of the UE so as to improve the data rate of the UE330. In the case of aggregating the downlink carriers or the uplinkcarriers of the eNB, this is referred to as intra-CA. In any case,however, there is a need of aggregating downlink carries or uplinkcarriers of the different eNBs.

A description is made of the inter-eNB CA adapted to the LTE systemaccording to an embodiment of the present disclosure hereinafter withreference to FIG. 4.

FIG. 4 is a diagram illustrating the concept of the inter-eNB CA adoptedto the LTE system according to an embodiment of the present disclosure.

Referring to FIG. 4, in the situation that the eNB 1 405 uses a carrierwith the center frequency of f1 for signal transmission/reception whilethe eNB 2 415 uses a carrier with the center frequency of f2, if thecarrier with the center frequency of f1 for signaltransmission/reception and the carrier with the center frequency of f2are aggregated for the UE, this means that the UE uses the carriers ofboth the eNB 1 405 and eNB 2 415 concurrently for signaltransmission/reception. In the present disclosure, this kind of CA isreferred to as inter-eNB CA. In the following description, the term‘Dual Connectivity (DC)’ is used interchangeably with the term‘inter-eNB CA.’

For example, if DC is configured, this means that inter-eNB CA isconfigured, one or more cell groups are configured, a Secondary CellGroup is configured, at least one Secondary Cell (SCell) under controlof an eNB which is not the service eNB is configured, a primary SCell(pSCell) is configured, a MAC entity for the Serving eNB (SeNB) isconfigured, or two MAC entities are configured at the UE.

The following definitions are provided to facilitate understanding ofcertain terms used frequently herein.

Assuming that a cell is configured with one downlink carrier and oneuplink carrier of an eNB according to the related art, the CA can beunderstood as if the UE communicates data via multiple cells. At thistime, the peak data rate and the number of aggregated carriers havepositive correlation.

In the following description, if the UE receives data through a certaindownlink carrier or transmits data through a certain uplink carrier,this means that the data are transmitted/received through the controland data channels of the cell corresponding to the center frequency andfrequency band defining the carrier. In the following description, CA isexpressed in a way that a plurality of serving cells are configuredusing the terms such as ‘primary serving cell (PCell)’, ‘secondaryserving cell (SCell)’, and ‘activated serving cell’. These terms havethe same meanings as used in the LTE mobile communication system. Itshould be noted that the terms ‘carrier’, ‘component’, and ‘servingcell’ are used interchangeably in the various embodiments of the presentdisclosure.

In the various embodiments of the present disclosure, a set of theserving cells under control of a same eNB is defined as a Cell Group orCarrier Group (CG). The cell group is categorized into one of a MasterCell Group (MCG) and Secondary Cell Group (SCG).

The MCG is a set of serving cells under the control of the eNBcontrolling the PCell (hereinafter, referred to as MeNB), and the SCG isa set of the serving cells under control of an eNB which is not theMeNB, i.e., a Slave eNB (SeNB). Whether a certain serving cell belongsto the MCG or SCG is notified to the UE by the eNB in the procedure ofconfigured the corresponding serving cell.

For one UE, one MCG and one or more SCGs can be configured and, althoughthe description here is directed to the case where one SCG is configuredfor explanation convenience in the various embodiments of the presentdisclosure, the present disclosure can also be applied equally to thecases where two or more SCGs are configured. The terms ‘PCell’ and‘SCell’ are used to indicate the types of the serving cells configuredto the UE. The PCell and SCell are different from each other in somerespects, e.g., the PCell always stays in the activated state while theSCell transitions between the activated and deactivated statesrepeatedly. The UE mobility is controlled in association with the PCell,and the SCell can be understood as a supplementary serving cell for datatransmission/reception. In an embodiment of the present disclosure, thePCell and SCell mean the PCell and SCell as defined in the LTE standardTS36.331 and TS36.321.

In the various embodiments of the present disclosure, a situation wherethe macro and pico cells coexist is assumed. The macro cell is a cellunder control of a MeNB and has a relatively large service area. Thepico cell is the cell under control of a SeNB and has a small servicearea in comparison to the macro cell. Although there is no strictcriterion to distinguish between the macro and pico cells, it may beassumed that the macro cell has a radius of about 500 meters and thepico cell has a radius of about a few dozen meters. In the followingdescription, the terms ‘pico cell’ and ‘small cell’ are usedinterchangeably.

Returning to FIG. 4, the eNB 1 405 is the MeNB, the eNB 2 415 is theSeNB, the serving cell 410 with the center frequency f1 is the servingcell 410 belonging to the MCG, and the serving cell 420 with the centerfrequency f2 is the serving cell 420 belonging to the SCG.

In the following description, the terms ‘MCG’ and ‘SCG’ may besubstituted by other terms. For example, the terms ‘primary set’ and‘secondary set’ or ‘primary carrier group’ and secondary carrier group′may be used instead of the terms ‘primary set’ and ‘secondary set.’ Itshould be noted that although the terms are different from each otherthey have the same meaning. The purpose of using such terms is todetermine whether a cell is under control of the eNB which controls thePCell of a specific UE 407, and the corresponding UE 407 and celloperate differently depending on whether it is under control of the eNBwhich controls the PCell.

Although one or more SCGs can be configured to a UE 407, it is assumedthat only one SCG is configured in the various embodiments of thepresent disclosure for explanation convenience. The SCG may include aplurality of SCells, and one of the SCells has special properties.

In the intra-eNB CA, the UE 407 transmits Hybrid ARQ (HARQ) feedback andChannel State Information (CSI) for the SCell as well as the HARQfeedback and CSI for the PCell through a Physical Uplink Control Channel(PUCCH) of the PCell. This aims to apply the CA operation to the UE 407having no capability of simultaneous uplink transmission.

In the inter-eNB CA, it may be actually impossible to transmit HARQfeedbacks and CSIs of the SCG SCells through PUCCH of the PCell. This isbecause the HARQ feedback has to be delivered in the HARQ Round TripTime (RTT) (typically 8 ms) but the transmission delay between the MeNBand SeNB may be longer than the HARQ RTT. For this reason, PUCCHtransmission resource is configured for one of the SCells belonging tothe SCG to transmit the HARQ feedbacks and CSIs for the SCG SCells. Theprimary SCell is referred to as pSCell. In the following description,the terms ‘inter-eNB CA’ and ‘DC’ are used interchangeably. Adescription is made of connection structures of a PDCP entity in the LTEsystem according to an embodiment of the present disclosure.

FIG. 5 is a diagram illustrating connection structures of a PDCP entityin the LTE system according to an embodiment of the present disclosure.

Referring to FIG. 5, a user service is provided through one EvolvedPacket System (EPS) bearer which is connected to one Radio Bearer. Thereis one PDCP and RLC per radio bearer and, in the inter-eNB CA, the PDCPentity and RLC entity of one radio bearer are located at different eNBsto improve data transmission/reception efficiency. At this time, it isnecessary to consider different approach depending on the type of theuser service.

In the case of the massive data service, it is possible to establish twoRLC entities to transmit/receive user service data to and from both theMeNB and SeNB as denoted by reference number 510. In the case of theservice demanding strict requirements such as Voice over LTE (VoLTE), itis possible to establish the RLC entity at only the MeNB so as totransmit/receive user service data through the serving cell of only theMeNB as denoted by reference number 505. It is also possible toestablish the bearer to transmit/receive data through the serving cellsof only the SeNB as denoted by reference number 535.

For explanation convenience, the bearer for transmitting/receiving datathrough the serving cells of only the MeNB as denoted by referencenumber 505 is referred to as MCG bearer, the bearer as denoted byreference number 510 is referred to as multi-bearer, and the bearer fortransmitting/receiving data through the serving cells of only the SeNBis referred to as SCG bearer. The PDCP entity of the MCG bearer or theSCG bearer is connected to one RLC entity, and the PDCP entity of themulti-bearer is connected to two RLC entities. The RLC entity fortransmitting/receiving data through MCG (or connected to the MAC entityassociated with the serving cells of the MCG) as denoted by referencenumbers 507 and 515 is referred to as MCG RLC entity, and the RLC entityfor transmitting/receiving data through the SCG as denoted by referencenumber 520 and 540 is referred to as SCG RLC entity. The MAC entityassociated with the data transmission/reception through the MCG asdenoted by reference number 509 and 525 is referred to as MCG MACentity, and the MAC entity associated with the datatransmission/reception through the SCG as denoted by reference number530 and 545 is referred to as SCG MAC entity. The MAC and RLC entitiesare connected through a logical channel and, in detail, the logicalchannel between the MCG RLC entity and the MCG MAC entity is referred toas MCG logical channel, and the logical channel between the SCG RLCentity and the SCG MAC entity is referred to as SCG logical channel. Forexplanation simplicity, it is assumed that the macro cell area is thearea where only the macro cell signal is received but the small cellsignal is not received, and the small cell area is the area where boththe macro and small cell signals are received. When the UE which demandslarge downlink data moves from the macro cell area to the small cellarea, it is possible to configure additional small cells to the UE and,among the bearers established for the UE, reconfigure the MCG bearercarrying large amount of downlink data such as File Transfer Protocol(FTP) as the multi-bearer or SCG bearer.

In order for the UE to operate correctly in a given communicationnetwork, it is necessary to report the information on the capability ofthe UE (hereinafter, referred to as capability information) to thenetwork (or at least one specific network node). The capabilityinformation may include the features and frequency bands supported bythe UE. As the UE improves in capability and integrates more and morenew features such as CA are introduced, the complexity and size of theUE capability information will also increase.

In order for a UE to report the DC capability to the network, itnecessary to check various types of information as follows:

-   -   Which band combinations are available for supporting DC?        Multi-bearer is supported?    -   SCG bearer is supported?    -   Which cell group combinations are supported?    -   Which serving cells are available for PUCCH transmission?

If the UE supports SCG bearer configuration, this means that the UE hasthe capability of encrypting and decrypting MCG bearer data with a firstsecurity key and encrypting and decrypting SCG bearer data with a secondsecurity key.

If the UE supports multi-bearer configuration, this means that the UEhas the capability of connecting one PDCP entity to two RLC entities totransmit/receive data.

The UE reports the information per band combination supporting DC asfollows:

-   -   Information indicating whether it supports the multi-bearer for        the corresponding band combination and has completed        Inter-Operability Testing (IOT) for the multi-bearer.    -   Information indicating whether it supports the SCG bearer for        the corresponding band and has completed IOT for the SCG bearer.    -   Information indicating whether it supports unsynchronized        network for the corresponding band combination.    -   Information indicating the serving cells of the corresponding        band combination which are available for PUCCH transmission        (hereinafter, referred to as PUCCH capability information).    -   Information indicating the serving cell group configuration        available for the corresponding band combination (hereinafter,        referred to as cell group capability information).

The IOT is testing interoperability between a UE and the network, and itis preferable to use only the functions which have passed the test.Since both the commercialized UE and the network are necessary for theIOT, if, although a certain function is implemented in the UE, it is notimplemented widely enough, the IOT may not be performed. Particularly inthe DC applied per band combination, if there is no network utilizingthe corresponding band combination yet or if, although any networkutilizes the corresponding band combination, it supports just one of theSCG bearer and multi-bearer, the IOT cannot be performed perfectly andeven the UE supporting both the SCG bearer and multi-bearer may be ableto perform IOT for one of the two in a certain band combination. If theUE does not report the IOT situation per bearer configuration, the eNBcannot check the bearer configuration to which the IOT has beenperformed such that the DC operation may be restricted. Thus the UE hasto generate the capability information including the information on thebearer configuration to which IOT has completed per band combination byreflecting the IOT situation.

The DC operation can be performed in a synchronized network (network inwhich the distance between subframe boundaries of downlink signals ofthe serving cells is less than a predetermined threshold, e.g., about 30micro seconds) or an unsynchronized network (network in which there isno restriction in distance between subframe boundaries of downlinksignals of the serving cells and thus the distance between subframeboundaries of downlink signals of the serving cells may increase up to500 micro seconds). Unlike the synchronized network for which thecapacity of the signal storage of the reception Radio Frequency (RF)circuit of the UE can be designed in consideration of only the timedifference, since the time difference of up to 0.5 ms should beconsidered in the unsynchronized network, the UE may be able to operatein the synchronized network or both the synchronized and unsynchronizednetworks. All the UEs supporting DC have to support the operation in thesynchronized network basically. Thus there is no need to indicatesynchronized network supportability explicitly. Since whether to supportunsynchronized networks depends on the UE, it is necessary to reportunsynchronized network supportability indication. Whether the UEsupports unsynchronized networks is indicated per band combination inassociation with IOT.

For DC operation, the UE has to have the capability of transmittingPUCCH through at least two serving cells. When the DC is supported in aband combination, the information indicating which serving cell of theband combination can be used to transmit PUCCH is referred to as PUCCHcapability information.

Since the PUCCH capability information about a band combinationindicates whether which two cells can be used for PUCCH transmissionamong the serving cell configurable in the corresponding bandcombination, as the number of band entries included in the bandcombination increases and as the bandwidth class (see TS36.101 andTS26.331) rises, the number of combination increases, and thusindicating which combinations can be used for PUCCH transmission one byone among all the combinations is likely to increase the signalingoverhead significantly. For example, assuming a band combination inwhich band X which is capable of configuring two serving cells, band Ywhich is capable of configuring two serving cells, and band Z which iscapable of configuring one serving cell; the number of cases forselecting 2 of the 5 serving cells is 20. In order for the UE toindicate one combination for PUCCH transmission among the 20combinations, 20-bit information is needed. By taking notice that a UEcan report up to 128 combinations, the overhead is too high to allow.

The present disclosure defines the most frequently used combinations,rather than taking all the cases into consideration, and associates theDC operation supportability. That is, if the UE has reported that itsupports DC in a certain band combination, this means that the UEsupports at least basic PUCCH capability in the band combination. Thebasic PUCCH capability means that the PUCCH can be transmitted (or PUCCHcan be configured) through the serving cells fulfilling a predeterminedcondition in ‘combination of two serving cells’ available in thecorresponding band combination. If PUCCH transmission is supported in acombination without the basic PUCCH capability, the UE reports thecapability information including extra information.

The combination corresponding to the basic PUCCH capability(hereinafter, referred to as basic combination) is defined depending onthe number of band entries (band parameter (BP), number of BPs) asfollows.

Basic combination of band combination with one band entry: all oftwo-cell combinations are basic combinations. For example, if a BandCombination Parameter (BCP) includes one band entry and the bandwidthclass of the band entry supports up to 3 serving cells, this means thatthe combinations of [cell 1+cell 2], [cell 1+cell 3], and [cell 2+cell3] are available and all of the three combinations allow for PUCCHconfiguration.

Basic combination for band combination with at least two band entries:combination of two serving cells belonging to different band entries isthe basic combination. For example, in the band combination consisted ofband X, band Y, and band Z; all of the two-serving cell combinationsconsisted of a band X serving cell and a band Y serving cell, all of thetwo-serving cell combinations consisted of a band X serving cell and aband Z serving cell, and all of the two-serving cell combinationsconsisted of a band Y serving cell and a band Z serving cell are basiccombinations. That is, all of the combinations, with the exception ofthe combinations consisted of the serving cells belonging to one entry,are basic combinations.

As described above, in the case of the band combination with one bandentry, the basic combination is the combination of the serving cells ofthe same band and, in the case of the band combinations with two or moreband entries, the basic combination is the combination of the servingcells of different bands.

For DC operation, two serving cell groups should be configured. If theDC is supported in a band combination, the information indicating theserving cells that can be sorted into the same serving cell group in theband combination is referred to as cell group capability information. Ifall combinations for the cell group capability information is definedand all per-combination supportabilities are reported, this willincrease signaling overhead significantly. In the present disclosure,configuring the cell groups in the combinations defined according to apredetermined rule is defined as basic cell group capability, and if aUE supports DC in a predetermined band combination, this means that theUE supports the basic capability too. That is, the UE checks thecombinations corresponding to the basic cell group capability in a bandcombination and reports, only when it supports the basic cell groupcapability, that it supports DC in the corresponding band combination.

The basic cell group capability is defined differently depending onwhether the number of band entries is one or two or more.

Basic cell group capability of band combination with one band entry:support all the cases configuring serving cells into two groups. Forexample, if a BCP includes one band entry and if the bandwidth class ofthe band entry supports up to 3 serving cells, all the cases of sortingcell 1 into a group and cells 2 and 3 into another group, sorting cells1 and 2 into a group and cell 3 into another group, and sorting cells 1and 3 into a group and cell 2 into another group are supported. Thismeans that all of the two-cell groups available in one band entry can beconfigured.

Basic cell group capability of band combination with two or moreentries: all cell groups, with the exception of the cases where theserving cells of one band entry are sorted into two serving cell groups,are basic cell groups. For example, the basic cell group capability ofthe band combination including band x, band y, and band z supports thecases of sorting the serving cells of the band x into one cell group andthe serving cells of the bands y and z into another cell group, sortingthe serving cells of the bands x and y into one cell group and theserving cells of the band z into another cell group, and sorting theserving cells of the bands x and z into one cell group and the servingcells of the band y into another cell group, but does not support thecase of sorting part of the serving cells of the band x into one cellgroup and remaining serving cells and the serving cells of the bands yand z into another cell.

FIG. 6 is a diagram illustrating a configuration of UE capabilityinformation for DC according to an embodiment of the present disclosure.

Referring to FIG. 6, the multi-bearer supportability and SCG bearersupportability form are formed as per-UE information, and the DCsupportability is formed as per-band combination information.

The UE capability information includes UE-supporting band combination(SupportedBandCombinationList) 608, DC band combination information(DCbandcombinationParameter) 635, and DC capability information(dualConnectivityCapability) 630.

The SupportedBandCombinationList 608 includes one or more BCPs(BandCombinationParameters; BCP) 610, 615, 620, and 625. The BCP is theinformation on the band combination supported by the UE. The BCPincludes one or more BPs (BandParameters; BP) 627, 628. The BP includesband indicator (FreqBandIndicator, not shown), downlink BP(bandParametersDL; BPDL), and uplink BP (bandParametersUL; BPUL). TheBPDL includes bandwidth class information (bandwidthClass, not shown)indicating a number of serving cells supported in the corresponding bandand antenna capability information. Bandwidth class A indicates thecapability capable of configuring one serving cell across the wholebandwidth up to 20 MHz, Bandwidth class B indicates the capabilitycapable of configuring two serving cells with total bandwidth of up to20 MHz, and Bandwidth class C indicates the capability capable ofconfiguring two serving cells with total bandwidth of up to 40 MHz.

The dualConnectivityCapability 630 includes the SCG bearer configurationsupportability information (ScgBearerSupport), multi-bearerconfiguration supportability information (SplitBearerSupport), andunsynchronized-network operation supportability (unsyncDeploySupport).The unsyncDeploySupport indicates whether the UE supports DC operationin two serving cells although the distance between a downlink subframe(subframe x) of a serving cell and a subframe (subframe y) closest tothe subframe x of the serving cell on the time axis among the downlinksubframes of another serving cell becomes equal to a predetermined value(e.g., 0.5 ms). That is, it indicates whether the UE supports DCoperation in the subframes x and y although the distance between theboundaries of the subframes x and y is widened up to 0.5 ms.

The DCbandcombinationParameter includes at least one DCsupported 640 or645, and the number of DCsupporteds is equal to the number of BCPs ofthe SupportedBandCombinationList. The DCsupporteds match BCPs one by onein order. For example, the first DCsupported 640 is the information onthe first BCP 610. If the DCsupported indicates ‘Yes’, this means thatthe UE supports DC in the band combination of the corresponding BCP andbasic PUCCH capability and basic cell group capability in thecorresponding band and has completed IOT in association with DC. At thistime, the details of the DC operation follows the indication of thedualConnectivityCapability. That is, if the dualConnectivityCapabilityindicates that the UE supports CSG bearer configuration and operation inthe unsynchronized network, this means that the above operation issupported in the band combination and the IOT related to the operationhas been completed.

FIG. 7 is a diagram illustrating a configuration of UE capabilityinformation for DC according to an embodiment of the present disclosure.

Referring to FIG. 7, the multi-bearer supportability and SCG bearersupportability are signaled per band combination.

The UE capability information includes UE-supporting band combination(SupportedBandCombinationList) 608 and DC capability information(dualConnectivityCapability) 730.

The dualConnectivityCapability includes one or more DC capability(DCCapability) 745 and 750. The number of DCCapability informations isequal to the number of BCPs fulfilling a predetermined condition. Thepredetermined condition is associated with CA and includes at least twoBPs (BandParameter) or band entries, or a BCP including a band entry ofwhich bandwidth class is not A, or the BCP includes at least two bandentries.

The DCCapability corresponds to the BCP fulfilling the condition in theorder of the arrangement of the BCP. For example, DCCapability 745corresponds to the BandCombinationParameters 620, and the DCCapability750 corresponds to the BandCombinationParameters 625.

The DCCapability includes at least 4 types of information. The firstinformation indicates whether the DC is supported on the correspondingband, the second information indicates whether bearer configuration issupported and IOT has been performed, the third information indicateswhether multi-bearer is supported and IOT has been performed, and thefourth information indicates whether unsynchronized network operation issupported and IO has been performed. If the first information is set to‘support’, this means that the UE supports DC on the corresponding band.In more detail, this means that the ‘basic PUCCH capability’ and ‘basiccell group capability’ are supported in the corresponding bandcombination.

If the second information is set to ‘support’, this means that the UEsupports SCG bearer configuration in the corresponding band combinationand the IOT for the SCG bearer configuration has been completed.

If the third information is set to ‘support’, this means that the UEsupports multi-bearer configuration in the corresponding bandcombination and the IOT for the multi-bearer configuration has beencompleted.

If the fourth information is set to ‘support’, this means that the UEsupports unsynchronized network operation in the corresponding bandcombination and the IOT therefor has been completed.

FIG. 8 is a signal flow diagram illustrating a DC configuration methodaccording to an embodiment of the present disclosure.

Referring to FIG. 8, in a mobile communication system including a UE805, an MeNB 810, an SeNB 813, and an MME 815. The UE 805 powers on atoperation 820. The UE 805 searches for the cells transmitting electricwave and a Public Land Mobile Network (PLMN) and determines the PLMN andthe cell for performing an attach process at Cell Search operation 825.

The UE 805 performs a Radio Resource Control (RRC) connection setupprocess and then sends the MME 815 a control message requesting forregistration (ATTACH REQUEST) at operation 830. The ATTACH REQUESTincludes a UE identifier. If the ATTACH REQUEST is received, the MME 815determines whether to accept the request and, if it is determined toaccept, sends the serving eNB (MeNB) 810 of the UE a control message(Initial Context Setup Request) at operation 835. If the MME has the UEcapability information, the Initial Context Setup Request message mayinclude the UE capability information, but the MME has no UE capabilityinformation in the initial attach process. If the Initial Context SetupRequest message including no UE capability information is received, theMeNB 810 sends the UE 805 a control message (UE CAPABILITY ENQUIRY) atoperation 840. The UE CAPABILITY ENQUIRY message is a message forrequesting the UE to report UE capability with a parameter call RadioAccess Technology (RAT) Type enquiring specific RAT capability of theUE. If the UE is performing the above procedure in an LTE network, theRAT Type is set to Evolved Universal Terrestrial Radio Access (EUTRA).If there is another type of radio network such as UMTS network, the MeNB810 may request the UE for the UMTS capability information by adding anRAT Type set to UTRA for preparing handover afterward.

If the UE CAPABILITY ENQUIRY message is received, the UE 805 generates aUE CAPABILITY INFORMATION message including its capability informationabout the radio technology indicated by the RAT Type. This messageincludes one or more band combination information per band combinationsupported by the UE 805. The band combination information indicates theCA combination supported by the UE, and the MeNB 810 configures anappropriate CA to the UE 805 based on this information. The UECAPABILITY INFORMATION message includes the UE's DC capabilityinformation, and the UE 805 configures the DC capability information inconsideration whether it supports DC supportability per bandcombination, whether IOT has been performed, and whether it supportsbasic capabilities.

The UE 805 sends the MeNB 810 a UE CAPABILITY INFORMATION message atoperation 845. The MeNB 810 forwards the UE CAPABILITY INFORMATIONmessage to the MME 815 at operation 850. The MeNB 810 reconfigures theUE 805 appropriately by referencing the traffic condition or channelcondition of the UE 805 based on the capability information reported bythe UE 805. For example, the MeNB 810 configures additional SCell or DCoperation to the UE 805. The DC operation is configured in considerationof the UE's DC capability. For example, the MeNB 810 determines bandcombination for DC, cell groups, PUCCH, and bearers by referencing theDC capability reported by the UE 805. The MeNB 810 sends an RRCConnection Reconfiguration message at operation 855.

Once the DC is configured, the UE 805 performs data communication withthe MeNB 810 and the SeNB 813 simultaneously at operation 860.

FIG. 9 is a flowchart illustrating a UE capability report procedure inthe DC configuration method of FIG. 8 according to an embodiment of thepresent disclosure.

Referring to FIG. 9, if a UE CAPABILITY ENQUIRY message is received atoperation 905, the UE checks the RAT Type included in the message atoperation 910. In an alternative embodiment of the present disclosure,the UE determines to report capability information according to apredetermined condition and then the procedure goes to operation 920.

If the RAT Type is set to EUTRA, the procedure goes to operation 920and, otherwise, operation 915. At operation 915, the UE operatesaccording to the related art. At operation 920, the UE performs theoperation for transmitting the UE CAPABILITY INFORMATION messageincluding its capability information generated as described above to theeNB. The UE capability information includes SupportedBandList,SupportedBandCombinationList, and DCbandcombinationParameter coded withASN.1; and the UE configures the information in consideration of theband combinations supporting DC along with information on whether IOThas been performed in the band combinations, basic PUCCH capability inthe corresponding combination, and basic call group capabilitysupportability.

The UE generates the UE CAPABILITY INFORMATION message including theabove information and sends this message to the eNB at operation 925. Atthis time, although there is any user data (e.g., IP packet or voiceframe) occurred previously, the UE transmits the UE CAPABILITYINFORMATION message with priority.

Second Embodiment

The second embodiment of the present disclosure is directed to the UEoperation when downlink or uplink failure occurs at the UE to whichmulti-bearer is configured. The downlink failure means a situation inwhich the downlink channel state level of a serving cell which is equalto or less than a predetermined threshold continues over a predeterminedduration, and the uplink failure means a situation in which randomaccess failure occurs in a serving cell. If the downlink or uplinkfailure occurs in the PCell, this means that Radio Link Failure (RLF)occurs; and if the downlink or uplink failure occurs in the pSCell, thismeans that SCG-RLF occurs. If the downlink or uplink failure occurs atthe UE to which multi-bearer is configured, the UE changes the uplinktransmission configuration of the multi-bearer by itself to minimizeuplink transmission termination.

FIG. 10 is a flowchart illustrating a UE operation according to thesecond embodiment of the present disclosure.

If RLF occurs at operation 1005, the procedure goes to operation 1010.If RLF occurs, this means that downlink or uplink failure occurs in thePCell or pSCell.

The UE determines whether the RLF has occurred in the MCG (or PCell) oran SCG (or pSCell) at operation 1010. If the RLF has occurred in the MCG(or PCell), the procedure goes to operation 1015 and, otherwise if theRLF has occurred in the SCG (or pSCell), the procedure goes to operation1020.

At operation 1015, the UE releases all of the MCG and SCG serving cellsand starts an RRC Connection Reestablishment procedure. The RRCConnection Reconfiguration procedure is the procedure of releasing thecurrent RRC connection and searches for a new serving cell to establishan RRC connection as specified in TS36.331.

At operation 1020, the UE determines whether the currently configuredbearers include any multi-bearer. If any multi-bearer exists, theprocedure goes to operation 1025 and, otherwise, the procedure goes tooperation 1040.

At operation 1020, the UE determines whether the downlink split ratio(percentage) of the multi-bearer is 100:0; and if so, the procedure goesto operation 1040 and, otherwise the procedure goes to operation 1030.The uplink split ratio is the ratio between the numbers of PDCP PDUstransmitted through the MCG and SCG and notified from the eNB to the UEin configuring the multi-bearer. If the uplink split ratio is 100:0,this means that all (100%) of the PDCP PDUs are transmitted through theMCG while the non-PDCP signal such as RLC control signals is transmittedthrough the SCG.

If the procedure goes to operation 1030, this means that the uplinksplit ratio is not 100:0 and all or part of the PDCP data aretransmitted through the SCG. For example, if the uplink split ratio is0:100, this means that the all of the PDCP data are transmitted throughthe SCG. The UE adjusts the uplink split ratio to a predetermined valuee.g., 100:0, at operation 1030. That is, the UE adjusts the uplink splitratio such that all of the PDCP data are transmitted through the MCG.

Then the UE triggers a Buffer Status Report (BSR) by means of aMultimedia MAC (M-MAC) entity at operation 1035. In the DC operation,two MAC entities are established in the UE: M-MAC entity associated withthe MCG and S-MAC entity associated with the SCG.

If the M-MAC entity triggers the BSR, this means that the UE generates aBSR as a control message indicating data amount available currently forthe UE and transmits the BSR through the MCG. Since adjusting the uplinksplit ratio at operation 1030 may change the data amount transmittedthrough the MCG, the UE triggers BSR by means of the M-MAC entity tonotify the MeNB scheduler of this quickly.

The UE stops monitoring PDCCH for the SCG serving cells and uplinktransmission through the SCG serving cells at operation 1040. The UEalso discards the uplink and downlink data stored in the HARQ buffers ofthe SCG serving cells.

Third Embodiment

The third embodiment of the present disclosure is directed to the UEoperation when the Timing Advance (TA) timer of the UE to which DC isconfigured expires. The UE determines the action it takes based on theTA Group (TAG) identifier of the TAG of which TA timer has expired.

A TAG is a set of serving cells sharing a same uplink transmissiontiming. A TAG is categorized into one of Primary TAG (P-TAG) andSecondary TAG (S-TAG). The P-TAG is the TAG including the PCell, and theS-TAG is the TAG including SCells with the exception of the PCell. If aserving cell belongs to a TAG, the uplink transmission timing of theserving cell is identical with the uplink transmission timings of theother serving cells belonging to the TAG and the uplink synchronizationof the serving cell is determined based on the TA time of the TAG.

The uplink transmission timing of a TAG is determined through a randomaccess procedure in a serving cell of the TAG and maintained byreceiving a TA command. Whenever the TA command is received in a TAG,the UE starts or restarts the TA timer of the corresponding TAG. If theTA timer expires, the UE determines that the uplink transmissionsynchronization of the corresponding TAG is lost and thus suspendsuplink transmission until the random access is performed again.

Each TAG is allocated a TAG identifier which is an integer in the rangefrom 0 to 3.

The UE operating in the DC mode may be configured with at least two TAG.Since the TAG is established per eNB independently, not all of theserving cells can be grouped in one TAG.

In the present disclosure, the MeNB and SeNB configure such that thePCell and pSCell belong to different TAGs and allocate a TAG identifierof 0 to the TAGs to which the PCell and pSCell belong respectively.

The UE operates the TA timer per TAG and, if a TA command is receivedthrough a serving cell, applies the TA command to the TAG indicated bythe TA identifier in the TA command and restarts the TA timer of thecorresponding TAG. At this time, the UE determines the TAG associatedwith the TA command in consideration of the serving cell group includingthe serving cell through which the TA command is received. For example,if the TA command is received through the SCG, the UE applies the TAcommand to the TAG having the identifier matching the identifierincluded in the TA command among the TAGs comprised of the SCG servingcells. For example, if a TA command with the TAG identifier of 0 isreceived through the MCG, the TA command is associated with a TAGincluding the PCell; and if a TA command with the TAG identifier of 0 isreceived through the SCG, the TA command is associated with the TAGincluding the pSCell.

FIG. 11 is a flowchart illustrating a UE operation when the TA timer ofa TAG expires (i.e., no TA command is received while the TA timer isrunning) according to an embodiment of the present disclosure.

A timeAlignmentTimer (TAT) expires at a certain timing at operation1105. The TAT is set per TAG. The TAT of a TAG starts first in theinitial random access procedure of the TAG and restarts whenever a TAcommand for the TAG is received. While the TAT does not run, the uplinksignal transmission, with the exception of the preamble transmission, isprohibited in the corresponding TAG. If the TAT expires, this means thatno TA command has been received for the TAG during the period defined bythe TAT.

The UE flushes the HARQ buffers of the serving cells belonging to thecorresponding TAG at operation 1110. This is done to preventnon-adaptive HARQ retransmission from being performed in thecorresponding SCell.

The UE determines whether the TAG identifier is 0 at operation 1115. Ifthe TAG identifier of the TAG of which TAT has expired is not 0, theprocedure goes to operation 1120 for the first procedure and, otherwiseif the TAG identifier is 0, operation 1125 for the second procedure.

The first procedure is taken when the TAT of the TAG through which PUCCHis transmitted is expired and, in this procedure, the UE releases thePUCCH and SRS transmission resources of a cell of the cell groupincluding the TAG and stops the TATs of the rest TAGs of the cell groupincluding the TAG. The UE flushes the HARQ buffers of all serving cellsof the cell group including the TAG. This is done to prevent any uplinktransmission from being performed in the corresponding cell group. IfSemi-Persistent Scheduling (SPS) is configured, the UE stops the SPS.That is, the configured uplink grant and downlink assignment arereleased. SPS is a technique of allocating transmission resourcesemi-persistently to minimize transmission resource allocation signaloverhead for service generating small packets periodically such as VoIPand thus, if transmission resource is allocated once, it can be useduntil a predetermined control signal is received or a predeterminedcondition for releasing the resource is fulfilled.

The second procedure is taken when the TAT of the TAG through which noPUCCH is transmitted expires and, in this procedure, the UE stops SRStransmission in the serving cells belonging to the TAG and releases theSRS transmission resource.

The procedure goes from operation 1120 to operation 1130 to apply rule 1to determine whether to perform uplink transmission in a serving cell.

The procedure goes from operation 1125 to operation 1135 to apply rule 2to determine whether to perform uplink transmission in a serving cell.

Rule 1: Do not prohibit uplink transmission in the cell groups with theexception of the cell group including the TAG of which TAT has expired,and prohibit uplink transmissions with the exception of predetermineduplink signal in the cell group including the TAG of which TAT hasexpired. The uplink transmission prohibition is released upon restart ofthe TAT. The predetermined uplink signal is the random access preamblesignal of the pSCell in the TAG belonging to the SCG or the randomaccess preamble signal of the PCell in the TAG belonging to the MCG.

Rule 2: Do not prohibit uplink transmission in the serving cells withthe exception of the serving cells belonging to the serving cellsbelonging to the TAG of which TAG has expired and prohibit uplinktransmissions with the exception of predetermined uplink signal for theserving cells belonging to the TAG of which TAT has expired. The uplinktransmission prohibition is released upon restart of the TAT. Thepredetermined uplink signal is the random access preamble signal.

In an alternative embodiment of the present disclosure, the UEdetermines whether difference between the uplink subframes boundaries ordifference between uplink transmissions timings of cell groups isgreater than a predetermined threshold value and, if so, reports thedetermination result to the eNB.

FIG. 12 is a flowchart illustrating another UE operation according tothe third embodiment of the present disclosure.

Referring to FIG. 12, the UE reports its capability in response to acontrol message requesting for UE capability report at operation 1205.As described above with reference to operations 840 and 845, the UE mayreport the information whether it supports DC per band combination andreports unsynchronized network operability (unsynchronized operationsupportability) per DC-supporting band combination.

The eNB configures DC of the UE at operation 1210. The UE configures MCGand SCG according to the instruction of the eNB and performs downlinkreception and uplink transmission.

The UE determines whether the difference between uplink transmissiontimings of the TAGs in the course of uplink transmission through the MCGand SCG at operation 1213. For example, the UE determines whether thedifference between the uplink transmission timing of a TAG (or uplinksubframe boundary) and the uplink transmission timing of another TAG (oruplink subframe boundary) is greater than a threshold value. The twosubframes being compared are the subframes overlapped most frequently onthe time axis. The transmission timing (or uplink subframe boundary) ofthe TAG is adjusted when the UE receives a TA command from the eNB andthus, when the TA command for a TAG is received form the eNB, the UEadjusts the uplink transmission timing according to the command anddetermines whether the difference between the adjusted timing and thetransmission timing of another TAG is greater than predetermined time.The predetermined time may be set, for example, to about 32 μsec.

If the difference between the transmission timings of the two TAGs (ordifference between the subframe boundary of the first TAG and the uplinksubframe boundary of the secondary TAG which is closest to the uplinksubframe boundary of the first TAG) is greater than the predeterminedvalue, the procedure goes to operation 1215.

Since the difference between the transmission timings of the two TAGs isgreater than the threshold value, the UE stops uplink transmission ofone of the two TAGs and sends the eNB a control message reporting thetermination of uplink transmission. At this time, in order to determinethe TAG in which the transmission is stopped and the information to bereported to the eNB, the UE checks the cell groups to which the two TAGsbelong, respectively, at operation 1215. If both the two TAGs belong tothe MCG, the procedure goes to operation 1220; if both the two TAGsbelong to the SCG, the procedure goes to operation 1225; and if one TAGbelongs to the MCG and another TAG belongs to the SCG, the proceduregoes to operation 1230.

At operation 1220, if the two TAGs include the P-TAG, the UE stopsuplink transmission in the TAG which is not the P-TAG. If the two TAGsinclude no P-TAG, the UE stops the uplink transmission of the TAG ofwhich uplink transmission timing difference with the P-TAG is greaterthan that of the uplink transmission of the other TAG. The UE generatesa control message including the identifier of the TAG in which theuplink transmission is stopped and the information indicating that theproblematic cell group is the MCG and transmits the control message tothe eNB.

At operation 1225, the UE determines whether the two TAGs include theS-TAG including the pSCell. If the two TAGs include the S-TAG includingthe pSCell, the UE stops the uplink transmission of the TAG which is notthe S-TAG including the pSCell. If the two TAGs include no S-TAGincluding the pSCell, the UE stops the uplink transmission of the TAG ofwhich uplink transmission timing difference with the S-TAG including thepSCell is greater than that of the uplink transmission of the other TAG.The UE generates a control message including the identifier of the TAGin which the uplink transmission is stopped and the informationindicating that the problematic cell group is a SCG and transmits thecontrol message to the eNB.

At operation 1230, the UE determines whether the band combination inwhich the current MCG and SCG are configured is a band combinationsupporting unsynchronized operation and, if so, continues the currentTAG operation at operation 1235. Otherwise if the band combination inwhich the current MCG and SCG are configured is a band combination notsupporting unsynchronized operation, the UE stops uplink transmission ofone of the two TAGs and transmits a control message to the eNB atoperation 1245. The control message includes the identifier of the TAGin which uplink transmission is stopped and the information on the cellgroup incurring the problem.

At operation 1230, the UE determines the TAG in which uplinktransmission is stopped as follows.

If the two TAGs include the P-TAG, the UE stops the uplink transmissionof the non-P-TAG. That is, the UE stops the uplink transmission of theTAG belonging to an SCG.

If the two TAGs include no P-TAG but S-TAG with the pSCell, the UE stopsthe uplink transmission of the S-TAG without pSCell, i.e., the uplinktransmission of the S-TAG of the MCG.

If the two TAGs include neither the P-TAG nor the S-TAG with pSCell, theUE stops the uplink transmission of the S-TAG belonging to the SCG.

In an alternative embodiment of the present disclosure, if the TAGsbelong to the same cell group, the UE stops the uplink transmission; andotherwise if the TAGs belong to different cell groups, the UE stops theuplink transmission and reports this to the MeNB. That is, if it occursthat the difference between the uplink transmission timings of the TAGsof the MCG is greater than a predetermined threshold, the UE stops theuplink transmission of one of the two TAGs; if it occurs that thedifference between the uplink transmission timings of the TAGs of theSCG is greater than a predetermined threshold, the UE stops the uplinktransmission of one of the two TAGs; and if it occurs that thedifference between the uplink transmission timings of the TAG of the MCGand the TAG of the SCG is greater than a predetermined threshold, the UEstops the uplink transmission of one of the TAGs and transmits a controlmessage to the eNB to report the situation.

In more detail, the UE stops the uplink transmission of the TAG which isnot the P-TAG at operation 1220 and terminates the procedure. (i.e., theUE flushes the uplink HARQ buffer of the serving cell belonging to theTAG which is not the P-TAG and releases the Sounding Reference Signaltransmission resource of the serving cell. If the UE flushes the HARQbuffer, this means that the data stored in the buffer are discarded).The UE stops the uplink transmission of the TAG which is not the P-TAGwith the pSCell and terminates the procedure at operation 1225.

At operation 1240, the UE stops the uplink transmission through the oneof the TAGs according to the above-described rule and transmits atransmission stop report message to the eNB. The transmission stopreport message may include the TAG identifier of the TAG in which theuplink transmission is stopped and N_TA. The N_TA is the informationspecifying uplink transmission timing, i.e., the time difference betweena predetermined downlink subframe and uplink subframe. For furtherdetails of N_TA, see TS36213. The transmission stop report message istransmitted to the MeNB through a serving cell of the MCG. If the TAG inwhich the uplink transmission is stopped is a TAG with the pSCell (i.e.,if the transmission timing difference between the P-TAG and the TAG withthe pSCell is greater than a predetermined threshold), the UE flushesthe uplink HARQ buffers of all the serving cells belonging to the SCG,releases the Sounding Reference Signal transmission resources of all theserving cells belonging to the SCG, and releases the PUCCH and CSItransmission resources configured to the pSCell. If the TAG in whichuplink transmission is stopped is an S-TAG without the pSCell, the UEflushes the uplink HARQ buffers of all the serving cells belonging tothe corresponding TAG and releases the Sounding Reference Signalsconfigured to the serving cells belonging to the TAG.

Fourth Embodiment

The fourth embodiment of the present disclosure is directed to the UEoperation in which the UE operating in the DC mode activates an SCell.The activation/deactivation of an SCell is indicated by means of theActivation/Deactivation (A/D) MAC Cyclic Extension (CE) (see TS36.321).Typically, an SCell is configured by means of an RRC control message ina deactivated state initially and then activated by means of the A/D MACCE indicating activation of the SCell. Meanwhile, if the pSCell isactivated by means of the A/D MAC CE, this causes a problem of delayingthe random access procedure in the pSCell. In the present disclosure,the UE activates the pSCell when the RRC control message for configuringthe pSCell (or RRC control message including pSCell configurationinformation) is received while it activates an SCell which is not pSCellwhen the A/D MAC CE is received. In the following description, thepSCell activation procedure is referred to as the first type activationprocedure, and the normal SCell activation procedure is referred to asthe second type activation procedure.

Table 1 specifies the first and second types activation procedures indetail.

TABLE 1 First type activation procedure Second type activation procedureInitiated by receipt of RRC control Initiated by receipt of MAC messagecontrol message Report CSI after starting PDCCH Start PDCCH monitoringafter monitoring initiating CSI report The UE starts random access inthe Since the CSI report is performed pSCell after completing in thePCell or the pSCell other preparation for the pSCell than thecorresponding SCell and activation. The UE monitors the eNB does notknow when the CSI PDCCH for random access and report is started, the UEstarts starts CSI report after completing CSI report without completionof the random access procedure. the SCell activation and monitors PDCCHupon activation of the SCell.

Monitoring PDCCH of an SCell may have the same meaning as receiving thePDCCH in the corresponding SCell and checking whether the schedulinginformation (downlink assignment or uplink grant) addressed to the CellRadio Network Temporary Identity (C-RNTI) of the UE is received.

Reporting CSI (see TS36.211, 36.212. and 36.213) for an SCell has thesame meaning as transmitting the control information indicating downlinkchannel status of the SCell through PUCCH. If the UE does not know thedownlink channel state of the corresponding SCell at the timing ofreporting CSI, it reports the CSI set to a predetermined value (e.g.,0).

The present disclosure defines the pSCell activation procedure and thenormal SCell activation procedure differently so as to improve the SCellactivation efficiency.

FIG. 13 is a flowchart illustrating the UE operation according to thefourth embodiment of the present disclosure.

The UE receives a control message indicating activation of an SCell at asubframe n at operation 1305. The control message may be an A/D MAC CEor an RRC control message including PCell activation information.

The UE determines whether the SCell to be activated is the pSCell atoperation 1310. If the SCell to be activated is the pSCell, theprocedure goes to operation 1325 and, otherwise, the procedure goes tooperation 1315.

The UE starts CSI report for the SCell at predetermined timing, e.g.,subframe n+8, at operation 1315. In more detail, the UE starts CSIreport for the SCell at the first subframe in which the Physical UplinkShared Channel (PUSCH) carrying CSI report for the SCell is configuredamong the subframes following the subframe n+8. The UE continues theactivation operation (e.g., RF reconfiguration for downlink signalreception and uplink signal transmission in the SCell) and, if theactivation is prepared completely, the procedure goes to operation 1320.

At operation 1320, the UE starts monitoring PDCCH of the SCell atsubframe n+k. Here, k is an integer which is equal to or greater than 8and less than a predetermined integer (e.g., 24) and which may be avalue indicating the subframe at (or right after) which the UE completespreparation for activating the SCell. The UE has to complete preparingactivation of the SCell at least before subframe n+k. Since k is aninteger equal to or greater than 0, the CSI report starts before thePDCCH report or at the same subframe as the PDCCH report.

The UE starts monitoring PDCCH of the SCell at the subframe n+x atoperation 1325. Here, x is a value indicating the subframe at which therandom access preamble is transmitted through the pSCell, the subframeat which a valid random access response message is received through thepSCell, or the 6th subframe since the subframe at which the valid randomaccess response message is received through the pSCell.

The UE performs the random access procedure and, if the random accessprocedure succeeds, the procedure goes to operation 1330.

At operation 1330, the UE starts CSI report for the SCell at thesubframe n+y. Here, y is a value indicating the first subframe at whichthe PUCCH is configured for CSI report for the SCell among the subframessince the time when the UE acquires the Master Information Block (MIB)(see TS36.331) of the pSCell.

Here, y is an integer greater than x. That is, the PDCCH monitoringstarts before the start time of the CSI report.

FIG. 14 is a block diagram illustrating a configuration of the UEoperating in an LTE system according to an embodiment of the presentdisclosure.

Referring to FIG. 14, the UE includes a control message processor 1465,upper layer processors 1470, 1475, and 1485, a controller 1480, anSCG-MAC entity 1415, a MCG-MAC entity 1410, a transceiver 1405, PDCPentities 1445, 1450, 1455, and 1460, and RLC entities 1420, 1425, 1430,1435, and 1440.

The transceiver 1405 receives data and predetermined control signalsthrough a downlink channel of a serving cell and transmits data andpredetermined control signal through an uplink channel. In the case thata plurality of serving cells are configured, the transceiver 1405transmits and receives data and control signals through the pluralityserving cells.

The MCG-MAC entity 1410 multiplexes data generated by the RLC entitiesor demultiplexes the data received by the transceiver 1405 and deliversthe demultiplexed data to appropriate RLC entities. The MCG-MAC entityprocesses the BSR or PHR triggered for the MCG.

The control message processor 1465 is an RRC layer entity whichprocesses the control message received from the eNB and takes anecessary action. For example, it receives an RRC control message andsends various configuration informations to the controller 1480.

The upper layer processor is established per service. The upper layerprocessor processes the user service data such as FTP and VoIP data andtransfers the processed data to the PDCP entity.

The controller 1480 checks the scheduling command, e.g., uplink grant,received by the transceiver 1405 and controls the transceiver 1405 and amultiplexer/demultiplexer to perform uplink transmission on appropriateresource at appropriate timing. The controller 1480 performs variouscontrol functions associated with the UE operations as described withreference to FIGS. 6 to 13. Although FIG. 14 is directed to the casewhere the UE is comprised of independent function blocks such as theMCG-MAC entity 1410, the control message processor 1465, various upperlayer processors 1470, 1475, and 1485, the controller 1480, the SCG-MACentity 1415, the MCG-MAC entity 1410, the transceiver 1405, the PDCPentities 1445, 1450, 1455, and 1460, and the RLC entities 1420, 1425,1430, 1435, and 1440; at least two of the MCG-MAC entity 1410, thecontrol message processor 1465, various upper layer processors 1470,1475, and 1485, the controller 1480, the SCG-MAC entity 1415, theMCG-MAC entity 1410, the transceiver 1405, the PDCP entities 1445, 1450,1455, and 1460, and the RLC entities 1420, 1425, 1430, 1435, and 1440may be integrated into one unit.

Also, the UE can be implemented with a transceiver for communicationwith at least one network node and a controller for controlling overalloperations of the UE. In this case, the controller controls to receive acontrol message indicating activation of at least one SCell, determinewhether the SCell to be activated is the pSCell based on the controlmessage, monitor, when the SCell to be activated is the pSCell, thePDCCH of the SCell, and report CSI through the SCell after starting thePDCCH monitoring.

The PDCCH monitoring start time may correspond to a subframe in whichthe UE starts transmitting a random access preamble through the pSCell,a subframe in which the UE receives a valid random access responsemessage through the pSCell, or a subframe after a predetermined numberof subframes since the subframe in which the valid random accessresponse message is received through the pSCell. The predetermined timemay be 6 subframes. The CSI report time may correspond to the firstsubframe for CSI report for the SCell after the time when the UEacquires the System Frame Number (SFN) of the pSCell.

If the SCell to be activated is not the pSCell, the controller controlsto report the CSI for the SCell and then monitor PDCCH of the SCell.

Although the descriptions are made of the individual function blocks ofthe UE for explanation convenience, the present disclosure is notlimited to the configuration as depicted in the drawing. Although thedescriptions are made of the functions and operations of the individualblocks, the control unit may control the operations of the UE asdescribed with reference to FIGS. 1 to 12 as well as the functions andoperations described with reference to FIG. 13.

A description is made of the configuration of the eNB operating in theLTE system according to various embodiments of the present disclosurehereinafter with reference to FIG. 15.

FIG. 15 is a block diagram illustrating a configuration of the eNBoperating in the LTE system according to an embodiment of the presentdisclosure.

Referring to FIG. 15, the eNB includes a MAC entity 1510, a controlmessage processor 1565, a controller 1580, a transceiver 1505, PDCPentities 1545, 1550, and 1555, RLC entities 1520, 1525, and 1530, and ascheduler 1590.

The transceiver 1505 transmits data and predetermined control signalsthrough a downlink carrier and receives data and predetermined controlsignals through an uplink carrier. In the case of a plurality ofcarriers are configured, the transceiver 1505 transmits and receives thedata and control signals through the plural carriers.

The MAC entity 1510 multiplexes data generated by the RLC entities 1520,1525, and 1530 or demultiplexes the data from the transceiver anddelivers the demultiplexed data to appropriate RLC entities and thecontroller 1580.

The scheduler 1590 allocates transmission resource to the UE at anappropriate timing in consideration of buffer status of the UE andchannel condition and controls the transceiver to receive and transmitsignals. The PDCP entities include the MCG bearer PDCP entities 1545 and1550 and the multi-bearer PDCP entity 1555. The MCG bearer PDCP entitytransmits/receives data through only the MCG and connects to one RLCentity. The controller 1580 controls the operations of the MeNB amongthe operations as described with reference to FIGS. 6 to 12.

Although FIG. 15 is directed to the case where the eNB is comprised ofindependent function blocks such as the MAC entity 1510, the controlmessage processor 1565, the controller 1580, the transceiver 1505, thePDCP entities 1545, 1550, and 1555, RLC entities 1520, 1525, and 1530,and the scheduler 1590; at least two of the MAC entity 1510, the controlmessage processor 1565, the controller 1580, the transceiver 1505, thePDCP entities 1545, 1550, and 1555, RLC entities 1520, 1525, and 1530,and the scheduler 1590 may be integrated into one unit.

Although the descriptions are made of the individual function blocks ofthe eNB for explanation convenience, the present disclosure is notlimited to the configuration as depicted in the drawing. Although thedescriptions are made of the functions and operations of the individualblocks, the control unit may control the operations of the eNB asdescribed with reference to FIGS. 1 to 13 as well as the functions andoperations described with reference to FIG. 15.

As described above, the SCell activation method and apparatus of thepresent disclosure is advantageous in terms of facilitating inter-eNB CAso as to improve transmission/reception data rate in a mobilecommunication system supporting DC.

Also, the SCell activation method and apparatus of the presentdisclosure is advantageous in terms of improving thetransmission/reception data rate of the UE through inter-eNB CA in amobile communication system supporting DC.

The above-described aspects of the present disclosure can be implementedin the form of computer-executable program commands stored in acomputer-readable storage medium. The computer-readable storage mediumis a data storage device capable of storing the data readable by acomputer system. Examples of the computer-readable storage mediuminclude Read-Only Memory (ROM), Random-Access Memory (RAM), Compact Disc(CD) ROM, magnetic tape, floppy disc, optical data storage devices, andcarrier waves (such as data transmission through Internet). Thecomputer-readable storage medium may be distributed to the computersystems connected through a network such that the computer-readablecodes are stored and executed in a distributed manner. The functionalprograms, codes, and code segments for implementing the presentdisclosure can be interpreted by the programmers skilled in the art.

The apparatus and method according to an embodiment of the presentdisclosure can be implemented by hardware, software, or a combinationthereof. Certain software can be stored in volatile or nonvolatilestorage device such as ROM, memory such as RAM, memory chip, andintegrated circuit, and storage media capable of recordable optically ormagnetically or readable by machines (e.g., computer) such as CD,Digital Versatile Disc (DVD), magnetic disc, and magnetic tape. Themethod according to an embodiment of the present disclosure can beimplemented by a computer or a mobile terminal including a controllerand a memory, and the memory is a storage medium capable of storing andreading the program or programs including the instructions implementingthe various embodiments of the present disclosure.

Thus the present disclosure includes the programs including the codesfor implementing the apparatus and method specified in a claim of thepresent disclosure and a non-transitory machine-readable(computer-readable) storage media capable of storing the program andreading the program.

The apparatus according to an embodiment of the present disclosure mayreceive the program from a program providing device connected through awired or wireless link and store the received program. The programproviding device may include a program including instructions executinga pre-configured contents protection method, a memory for storinginformation necessary for the contents protection method, acommunication unit for performing wired or wireless communication with agraphic processing device, and a controller for transmitting a requestof the graphic processing device or the corresponding programautomatically to the transceiver.

While the present disclosure has been shown and described with referenceto various embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present disclosure asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A Secondary Cell (SCell) activation method of aterminal supporting dual connectivity, the method comprising: receivinga control message instructing activation of at least one SCell;determining whether the SCell is a primary SCell (pSCell) based on thecontrol message; monitoring, when the SCell is the pSCell, a PhysicalDownlink Control Channel (PDCCH) of the pSCell; and reporting, afterstarting PDCCH monitoring, Channel Status Information (CSI) for theSCell.
 2. The method of claim 1, further comprising: reporting, when theSCell is not the pSCell, the CSI for the SCell; and monitoring, afterreporting the CSI, the PDCCH of the SCell.
 3. The method of claim 1,wherein the monitoring of the PDCCH starts at one of a subframe in whichthe terminal starts transmitting a random access preamble through thepSCell, a subframe in which the User Equipment (UE) receives a validrandom access response message through the pSCell, a subframe after apredetermined time elapses since a subframe in which a valid randomaccess response message is received through the pSCell.
 4. The method ofclaim 3, wherein the predetermined time is 6 subframes.
 5. The method ofclaim 1, wherein the reporting of the CSI starts at a first subframereserved for CSI report for the SCell after detecting a System FrameNumber (SFN) of the pSCell.
 6. A Secondary Cell (SCell) activationapparatus of a terminal supporting dual connectivity, the apparatuscomprising: a transceiver configured to communicate with at least onenetwork node; and a controller configured to control the transceiver toreceive a control message instructing activation of at least one SCell,to determine whether the SCell is a primary SCell (pSCell) based on thecontrol message, to monitor, when the SCell is the pSCell, a PhysicalDownlink Control Channel (PDCCH) of the pSCell, and to report, afterstarting PDCCH monitoring, Channel Status Information (CSI) for theSCell.
 7. The apparatus of claim 6, wherein the control unit isconfigured to report, when the SCell is not the pSCell, the CSI for theSCell and monitors, after reporting the CSI, the PDCCH of the SCell. 8.The apparatus of claim 6, wherein the controller is configured to startmonitoring the PDCCH at one of a subframe in which the terminal startstransmitting a random access preamble through the pSCell, a subframe inwhich the User Equipment (UE) receives a valid random access responsemessage through the pSCell, and a subframe after a predetermined timeelapses since a subframe in which a valid random access response messageis received through the pSCell.
 9. The apparatus of claim 8, wherein thepredetermined time is 6 subframes.
 10. The apparatus of claim 6, whereinthe controller is configured to report the CSI at a first subframereserved for CSI report for the SCell after detecting a System FrameNumber (SFN) of the pSCell.